1. Field of the Invention
The present invention relates to semiconductor circuit boards and, more particularly, to a system and method for calculating material density variations in multi-layer printed circuit boards.
2. General Background
Material, such as copper, density variation analysis is performed in the semiconductor industry as a metric for determining manufactured semiconductor board quality. Calculating the density variations for designing the printed circuit board is often required in the manufacturing process to assess manufacturing defects. Specifically, larger the variation in material density the more likely the board will exhibit mechanical and thermal defects. Thus, the density variation analysis is used for the purpose of making copper pattern density substantially uniform across the board.
One mechanism to determine material density variation is through the use of ultra-violet light and glass based system 1 as shown in FIG. 1. Shown therein, is a bottom and top glass exposure layers 2 and 4 respectively. Sandwiched between these layers are a top and a bottom photo-tool layers 6 and 8 respectively. The photo-tool layers 6 and 8 are brought in contact with the multi-layer printed circuit board 10 having material (e.g., copper) variations, generally depicted as 12 and 14. An ultra-violet light is transmitted from one end 16 towards a sheet of material (not shown) positioned at another end 18. The interference pattern observed on the sheet material provides feedback means for identifying material variations on the printed circuit board. However, there are several disadvantages with this system including, (i) the system being expensive, (ii) the need for contacting the multi-layer printed circuit board with the photo-tools/exposure glass system thereby increasing the likelihood of damaging the circuit board.
Density variation analysis is useful for determining other important scalar properties, for example, defect susceptibility, power dissipation, etc. for purposes of modeling and/or correction for these properties. The density variation analysis also is used to estimate yield loss due to densities that are too low or too high in layers of the design. The density variation analysis may be used to evaluate non-uniformities in height across the circuit board due to variations in density. Density analysis may be anywhere from about 10% to about 50% for standard designs.
Therefore, a need exists for an efficient and cost-effective method for determining density variations of the material in a printed circuit board.